Skey. — 071 the Moi-emcntii of Camphor on Water. 403 



The effect of a gentle heat in obhterating photographic impressions (4) 

 is no doubt called into play, where, as Claudet observes, " exposure to the 

 red rays neutralizes the effect previously produced on a sensitive sui'face by 

 white light." 



From results Nos. 7, 8, 9, and 10, it is seen that these silver salts have a 

 predisposition to combine with small or even minute quantities of certain 

 substances, the same as molybdic acid and its congeners have in relation to 

 phosphoric acid, and this, without doubt, indicates a molecular change 

 throughout, and one which, at least in the case of argentic-iodide, is possibly 

 of the same nature in respect to structm-al form as that which light induces. 

 It has been ascertained by Vogel that in the case of this salt (argentic- 

 iodide) no silver or iodine is liberated by light — the change is molecular 

 only ; so that the experimental results detailed above may have a signifi- 

 cance in regard to the mode in which light produces this. But being a 

 change apparently of this character only, it is not a httle singular that 

 water, or its constituents, is necessary for its production ; and it was this 

 that led me to make experiment (5), under the idea that water is assimi- 

 lated by this salt when photograiihic effect takes place upon it. The result, 

 however, as is seen, does not show this to be the case ; but further experi- 

 ments seem necessary here. 



From the results last described (11, 12) it is seen that most oxidizing 

 substances have the property of putting argentic-iodide, altered by hght, 

 back to its normal state, and that this salt comports itself with ammonia 

 according as to whether light has been permitted to exert its influence 

 thereu2)on or not, results which have no doubt an intimate relation to the 

 phenomena under consideration, but in what way it is difficult as yet to 

 discover. The primary effect of ammonia, however, in the last result is, 

 it would seem, merely to form feebly ammoniacal compounds with the silver 

 salts, which are so unstable as to be decomposable by water. 



Art. LXII. — Further Notes upon the Movements of Camphor on Water. By 

 William Skey, Analyst to the Geological Survey Department. 

 [Read before the Wellington Philosophical Society, 21st February, 1880.] 

 Since my paper "On the Movements of Camphor on Water"* was read 

 before you, I have learned that this subject has been especially treated by 

 Professor Tomlinson, in one of a series of "experimental essays," dated 1863. 

 This work I cannot get hold of ; but the theory which this scientist there 



* Trans. N.Z. Inst., Vol. XI., p. 473. 



